Line lockout arrangement



Nbv. 11, 1952 J 013, SHEPHERD 2,617,888

LINE LOCKOUT ARRANGEMENT Filed April 1, 1950 9 Sheets-Sheet l N K56 mm"\O Q 993% Lkkk INVENTOR J. 0. SHEPHERD A T TORNEV Nov. 11, 1952 J. O'D.SHEPHERD LINE LOCKOUT ARRANGEMENT Filed April 1, 1950 4 TRUN/(S TRUNK l4LINES IN H30? 40/ sue sua sue sub -9 Sheets-Sheiet 2 .IAIIVENTOR J. 0.SHEPHLIRD ATTORA/F VENTOR ATTOHRNEY 9 Sheets-Sheet 3 SHEPHERD BY HUD $54 RWQQ J O'D SHEPHERD LINE LOCKOUT ARRANGEMEN'? QR QQM Nov. '1 1, 1952Flled Aprll l, 1950 NOV. 11, 1952 0'13, SHEPHERD 2,617,888

LINE LOCKOUT ARRANGEMENT Filed April 1, 1950 9 Sheets-Sheet 4 INVENTORJ. 0.$HEPHERD ATTORNEY FIG. 5

Nov. 11, 1952 n SHEPHERD 2,617,888

LINE LOCKOUT ARRANGEMENT Filed April 1, 1950 9 Sheets$heet 5 FIRST LINELAST LINE lNl EN 70/? -J. O. SHEPHERD ATTORNEY FIG. 6

9 She'ets$heet 6 Filed April 1, 1950 INVENI'OR J. 0. SHEPHERD flfl/ATTORNEV/ N 2 J. OD. SHEPHERD 2,617,883

LINE LOCKOUT ARRANGEMENT Filed April 1, 1950 9 Sheets-Sheet s F/RsrTRUNK /v v5/v TOP .1 0. SHEPHERD ATTORNEY FIG. 9

Nov. 11, 19 J. O'D. SHEPHERD 2,517,883

LINE LOCKOUT ARRANGEMENT Filed April 1, 1950 9' Sheets-Sheet 9 //v l/ENTOR J. 0. SHEPHERD A T TORNEV 'der the control of link circuits.

Patented Nov. 11, 1952 UNITED STATES rear race 2,617,888 LINE LQCKOUTARRANGEMENT Application April 1, 1950, Serial No. 153,453

(Cl. ire-22) 14 Claims.

The present invention relates generally to automatic telephone systemsand more particular to circuit means eliective automatically at timesfor preventin calling lines from initiating automatic switchinterconnections.

In automatic systems wherein subscribers lines and trunks terminate inswitches, such as crossbar switches, it is of course desirable toprevent double connections, which might occur if two such lines shouldset up a calling condition simultaneously or concurrently.

One of the main objects of the present invention is to provide circuitmeans associated with the line circuits of such lines which means areeffective automatically, when a plurality of lines set up callingconditions concurrently, to prevent any one 01 such lines from'effectingswitching operations until such one line disconnects.

In such automatic systems as are contemplated by the utility of thepresent invention, whenever a callin line effects a switchinterconnection such interconnection is arranged through or un- Theselink circuits are seized by calling lines for the purpose of completingthe desired interconnection, such interconnection, depending upon thenature thereof, as will be apparent from subsequent description, usinsaid links either only to set up the interconnection whereupon suchlinks are released or to control the interconnection throughout theensuing conversation period.

Another main object of the present invention is to provide circuit meansassociated with said links and with said lines which means are efiectiveautomatically, when all available links are busy, to prevent any callingline from effect'ing switching operations until such calling linedisconnects.

Other features, objects and purposes of the present invention willbeapparent from the subsequent detailed description of a preferredembodiment thereof.

The present invention is shown and described herein as embodied in asmall, simple community dial cross-bar office. Subscribers lines andtrunks, either incoming or outgoing, are terminated in verticals of across-bar switch; and, link circuits are terminated in horizontals ofthe same switch. Each link circuit occupies two horizontal units of thecross-bar switch in order to complete interconnections between linesterminating in the same switch. A common start circuit is provided forall links: this start circuit is -under the control of lock-out relaysin the various line circuits and or link assignment re- H laysassociated with the various 11hr circuits. According to th invention, iitwo or more lines should be placed concurrently into callin condition,the lock-out relays of all such lines will be operated thereby toprevent any one of such lines from controlling or attemptin to controlthe start circuit until such line disconnects and reinitiates a call.Likewise, according to the invention, should all links be busy when anyline is placed into a calling condition, the link assignment relaysassociated with such links will operate the lock-out relay of such line,thereby to prevent such line from controlling or attempting to controlthe start circuit until such line disconnects.

The present invention, outlined above, will be described in detailhereinafter in connection with the drawings which may be describedgenerally as follows:

Fig. 1 shows diagrammatically a cross-bar switch unit with four trunklines and fourteen subscribers lines terminated in Verticals thereof andfiv'e link circuits terminated in the ten horizontals thereof;

Fig. 3 shows four verticals and four horizontals, with associated holdand select magnets, of a cross-bar switch unit whereon are shown a firstand a last subscribers line and trunk line, and with line circuitterminations;

Figs. 4, 5, "7 and 8 Shower first and a last link circuit, the firstlink circuit being shown in detail;

Fig. 6 shows line circuits for the first and last subscribers lines; I VI Figs. 9 and 10 show respectively the line and supervisory circuits forthe first and last trunk lines; and,

Fig. 2 illustrates how the other figures may be arranged to disclose thepresent invention as embodied in the disclosed telephone system.

GENERAL DESCRIPTION The representation in Fig. 1 diagrammaticallyillustrates a cross-bar switch unit comprising twenty vertical units andten horizontal units. A plurailty of subscribers lines are terminated onsome of the verticals and a plurality of trunk circuits are terminatedon other verticals. Thus the hold magnets corresponding to theseverticals also correspond to the associated trunks and subscribers linesand will, when operated in conjunction with a select magnet, 'effe'ct aninterconnection between such line or trunk and a horizontal unit of theswitch, as is well known. The ten horizontal units of the switch areassociated with five link circuits on a paired basis. That is, each linkis terminated in two horizontal units designated In and Out in Fig. 1.Each of these horizontal units is, as is also well known, under thecontrol of a corresponding select magnet which, when operated,conditions the associated horizontal unit to be interconnected, underthe control of a hold magnet, with any vertical unit on the switchcorresponding to said hold magnet.

When a call is originated by one of the subscribers lines or is incomingover one of the trunks, an idle link circuit is assigned to the call.Interconnection between the line or trunk and such link is accomplishedover the In unit of said link. These types of calls use the link untildisconnection occurs. When the link knows the destination of the call(either to a line or to a trunk), the link, after testing that such pathis idle, connects therewith by means of the Out unit of said link.

In the event of a reverting call (a call between subscribers on the sameline terminating in the switch), a link is seized by means of its Inunit. The link effects the interconnection of the parties over such unitand then releases. Thus, this type of call does not use the link exceptto control the interconnection.

For calls between subscribers of different lines terminating in thisswitching unit, a three-digit number system is suggested. The first twodigits designate and identify the number of the line called. The thirddigit identifies the type of ringing required and the side of the lineto which it is to be applied. An arbitrary numbering sys- 1 tem has beenchosen to illustrate the principles of the present invention as embodiedin a system having fourteen lines, four trunks, and five links. Thenumbering plan in the assumed case is as follows:

Line 1-81 Line 57 5 Line 8-71 Line 12-85 Line 27'2 Line 6-76 Line 982Line 1387 Line 3-73 Line 77 7 Line 83 Line 148(i Line 474 Line 1184 Thereasons why such system has been chosen as preferable, while beingarbitrary, will be discussed somewhat hereinafter. On an eightpartysemiselective basis this unit can handle calls to, from, and betweensome 112 individual subscribers whose lines terminate in this switchingunit. In order to indicate to a subscriber when he is being called, fourringing codes are employed to be applied to the tip or ring side oftheline to select one out of eight possible subscribers on that line. Thesecodes will be selected by the third digit which may be one of the digits1, 2, 3, and 4.

Where the central ofiice which serves this switching unit is a manualoflice (the trunks terminating at the unit extend to a manual office),calls originated by subscribers to operators will be accomplished by thedialing of just one digit, a zero.

Where the central oifice to which this swtiching unit is connected is adial ofiice, an operator thereat may be reached by dialing zero,followed by another zero when the automatic equipment at such ofilce isready for this second directing digit zero. A subscriber in theaforesaid dial ofice may be reached by the switching unit subscriberdialing a zero followed by the number of the desired subscriber.

Calls from one switching unit to another through a dial central ofliceare accomplished by dialing zero, followed by a code dimq ing an etension of the connection to the desired switch-- ing unit, and followedby the three digits iden-- tifying the desired subscribers line andringing: condition thereat.

The description set forth hereinafter as a disclosure of a preferredembodiment of the present invention will provide detailed descriptionsof the following four types of calls, with, of course, other descriptivematter relating to details common to all such calls and relating todifferences as well:

(1) Local callDiiferent lines (2) Reverting call (3) Trunk callIncoming(4) Trunk call-Outgoing LOCAL CALLDIFFERENT LINESSAME SWITCHING UNITLine finding When a subscriber, say subscriber 3M, initiates a call byremoving his receiver from its normal position, a circuit is closed foroperating the line relay L('6) of the first line (the symbol L(B) meansrelay L in Fig. 6). Relay L06) of the first line operates in a circuitextending from ground, through the upper winding of relay L(B),conductor 6G0, contact 2 of hold magnet 11(3) of the first line, tipconductor 3%, over the closed subscriber loop, ring conductor 3S5.contact 3 of hold magnet H(3), conductor 39!, to battery through thelower winding of line relay L(6). Relay L(6) of the first line circuit,upon operating, closes a start circuit over conductor 69! to operaterelay RG16) of the first link circuit in a circuit extending fromground, over the contact of the line delay relay LDOS), contact of thelook-out relay (6) of the first line, contact 4 of relay L(6), conductor60!, contact 6 of the link assignment relay LI (4) of the first link,

conductor 00, to battery through the upper winding of relay RCI(5) Ifthe first link had been busy, relay Ll(i) would have been operated, aswill be explained hereinafter. In that situation, the circuit lasttraced for operating relay RCI(5) of the first link would have beenswitched over contact 1 of the operated relay LI (4), to a chain of suchrelays Ll(4) to L5(4), and over a contact correspending to contact 6 ofrelay LI (4) of the first unoperated relay to the group L2(not shown) toL5(4) to operate the relay RCI (not shown) of the first idle link.

In the event that all links are busy then all of the relays L(4) toL508) will be operated. The above start circuit extending over conductor'60! would be open at the last relay, such as L503), and another circuitwould be established for operating the lock-out relay L006) of thecalling line. This circuit may be traced from ground, over contact 3 ofrelay L5(4), over front contacts of relays L4 to L2 (not shown), contact 3 of relay LI(4), conductor 423, contact 5 of relay L(6) to batterythrough the lower winding of relay LO(6). Relay L006) operates and locksover its contact 3, contact 3 of relay L(6), to ground throughresistance LR(9). The operation of relay LO(6) opens, at its contact l,the above-traced start circuit. Thus, until subscriber 389 disconnects,to thereby release relay L(6) such subscriber's line circuit cannotagain attempt to seize an idle link circuit.

It will be assumed, for the purposes of the present discussion, that thefirst link is idle and that therefore relay LI (4) is released,permitting relay RCI(5) to operate as above described. Relay RCI( 5)upon operating, operates theselect magnet 18(3), associated with the Inhorizontal unitof the first link, in a circuit extending from ground,over contact 8 of relay RCI(5), conductor 580, contact 8 of relay LI(4),conductor dill, to battery through the Winding of select magnet IS (3).Select magnet IS(3-), upon operating, operates the hold magnet I-I(3)associated with the calling subscribers line in a circuit extending fromground, over the contact of select magnet 18(3), conductor 3132, contact4 of relay LIM), conductor 402, contact 2 of relay L(-6) of the firstline, contact I of the look-out relay LO(6) of the first line, conductor$02, to battery through the winding of bold magnet H(3). Theoperation-of hold magnet H(3) closes the cross-points determined by theoperation of the select and hold magnets described thereby tointerconnect the calling first line with the first link over the Intermination of said link. Hold magnet H(3) locks to ground supplied overthe contact of select magnet IS(3), conductor 3822, contact "I of relayLloi), sleeve conductor N3 of the switching unit, contact 3 of thecrosspoints, to battery through the winding or hold magnet I-I(-3).

Hold magnet H(3) upon operating, releases the line relay L('8) of thefirst line, leaving the hold magnet II(-3) locked operated as abovedescribed. The operation of hold magnet H(3) operates the look-out relayLO(6) of the first line in a circuit extending from ground on the sleeveill3 of the switching unit, over contact 3 of the cross-points, contactI of hold magnet I-I(3), conductor 301, to battery through the upperwinding of relay LO (6) of the first line.

When the cross-points of the switch are closed, relay AM) of the firstlink operates in a circuit extending from battery, through the lowerwinding of relay A(4), contact I of relay D(4), contact I of thecut-through relay CTM), tip conductor 404, contact I of thecross-points, tip conductor 304 of the calling first line, over the lineloop, ring conductor 3%, contact 2 of the cross-points, ring conductor3%, contact I3 of cut-"through relay CT(4) contact 3 of relay D(4),through the upper winding of relay A02) contact I of the dial tone relayDTot), conductor 405, to ground through the left winding of the dialtone transformer 5M. Relay AM), upon operating, operates relay 13(4) inan obvious circuit over contact 2 of relay A05).

Relay B(4), upon operating, completes a circuit for providing off-normalground at its contact 3. This off-normal ground operates the linkassignment relay LI (4) in a circuit over contact 3 of relay CTM), tobattery through the winding of relay LI (4). Relay LI (4), uponoperating, transfers at its contact I, as above described, the circuitover conductor Bill which operated relay RCI(5) so that the next call,if any, will operate the relay RCI (not shown) of the next idle linkcircuit. Relay LI t), upon operating, also connects the sleeve conductor503 if the switch to off-normal ground over its contact 2, contact 2 ofthe time-out relay T003), conductor 529,

7 contact 5 of relay CTUI), and over contact 3 of relay 3(6).

Line relay L05) of the first line, upon releasing, as above described,opens the operating circuit for relay RCI (5), which relay however, isslowreleasing and will not release until relay LIUl) has operated toapply off-normal ground to the sleeve conductor 3 of the switch. Uponthe operation of relay LI (4) theselect magnet 13(3) is released,leaving the connected cross-points of the switch under the solecontrolof hold magnet H(3).

Simultaneous calls lock-out If two or more lines are placed in a callingcondition simultaneously two or more line relays L-(Ii) will be operatedat the same time, such as relay L(6) for the first line and relay M6)for the last line. Each relay -L(6), upon operating, completes a circuitfrom ground, through its associated resistance LR(6), over its contact3, contact 2 of the associated lock-out relay LOGS), to battery throughthe winding of the marginal line supervisory relay LS6). Relay LS(6)will not operate if only one resistance LR(B) is in series therewith,but will operate if two or more such resistances LR(6) are in parallelbecause of two or more simultaneously operated line relays L(6). If twoor more lines, say the first line and the last line, operate theirrelays L(6) concurrently, relay 118(6) will operate. Relay 118(6), uponoperating, completes circuits for operating the look-out relays LO(6) ofall lines which are in a calling condition (relays L(B) operated)extending from ground, over the contact of relay L866), contact 5 of"each relay L03) which is operated, to battery through the lowerwindings of the associated lock-out relays LOGS). 'Ihose relays (6),which are thereby operated, are locked in circuits extending fromground, through resistance LRfli), contact 3 of relay LO(6), to batterythrough the upper winding of relay L005). The operation of these relaysLOiB) releases relay LS(6). These operated relays LO(6) open, at theircontacts 4, the previously traced start circuit over conductor GUI foreach such line. Until a calling subscriber "disconnects to release itslock-out relay LO(6), this lock-out condition prevents each suchsubscriber from being able to effect a connection with a link circuit.It will now 'be assumed that ther is no simultaneous call situationinvolved.

Link time-out It will be recalled that the holding ground on the sleeveconductor 403 of the switch is under the control of contact 2 of thetime-out relay TO(4). The time-out relay TOM), if operated, would removethis holding ground and release the connection between the calling firstline and the first link. Before relay LI(-4) operated, as abovedescribed, condenser T001), if charged, was discharged in a circuitextending from ground, through condenser TCUI), resistance TOM),resistance TRMZ), to ground over contact .II) of relay LIUZ). When relayLl( l) was operated, as above described, the ground .on contact l9 ofrelay Ll(4) was replaced by a high positive voltage (say about volts ofpositive direct-current voltage) from the rectifier bridge 502, throughlamp L( 5), conductor 593, to resistance TR M) over contact 9 of relay1.!(5). Condenser T'CM) begins to acquire a charge in this circuit andthe values of resistances TRUE) and T'Cfl) and condenser TC(4) are suchthat, if allowed to charge for about eight seconds (for illustration),condenser TC 4) will have acquired a charge sufiic'ient to causeionization of gas tube TTQ) between electrodes I and 2 thereof. Suchionization will effect a, discharge across tube TTG I) from ground,electrode 2 to electrode 3, winding of relay 'TO (4), contact 9 of relayLI,(4), conductor 503 to positive voltage. Relay TOM) 7 will thereuponoperate to discharge condenser TC(4) over its contact 3.

When relay TO(4) operates, it opens, at its respective contacts 1 and 2,the sleeve conductors 308 and 403 of the Out and In units of the switchcorresponding to the first link. The opening of such sleeve conductors308 and 403 will of course release any operated hold magnets locked toground on such conductors thereby releasing the connection, if any.Relay TO (4) will remain operated until relay L1(4) releases.

There are many ways in which condenser TC(4) may be discharged before itacquires a charge suflicient to fire tube TT(4). Tube TT(4) is arrangedto be fired only if there has been excessive delay between variouscircuit operations. As will be apparent from subsequent description, theoperation of any one of the relays CT(4), D(4), C(4), or PU(5) withrelay RCO(5) released, will discharge condenser TC(4) to prevent atime-out.

If a time-out occurs, the hold magnet, such as hold magnet H(3) for thefirst line, will release, thereby reoperating the associated line relayL(6). Relay L(6), upon reoperating, will lock operated the lock-outrelay LO(6) over contact 3 of the latter to ground over contact 3 ofrelay L() and through resistance LR(), relay LO(0) being slow releasingto permit the reoperation of the line relay L(5) to lock relay LO(6)operated before the latter can release upon the release of theassociated hold magnet H(3). Relays A(4) and 3(4) of the link circuit,if operated as previously described, will of course release, with therelease of the switch interconnection, to thereby release relay L1 (4)If acall is abandoned at such a time as condenser TC(4) may haveacquired a partial charge, the release of relay L1(4), above described,will, at its contact 10, discharge condenser TC (4) Under normalprocedure of a call, the timeout arrangement will be disabled by theoperation of one or more of the above-mentioned relays CT(4), D(4),C(4), or PU(5) with relay RCO(5) released. It will be assumed that thesequence of circuit operation is timely, thereby to preclude a time-outas above described.

Line lock-out After the calling line has been found, relay LO(B) will beoperated as previously described. The operation of relay LO(6) withrelay L(6) released, opens at contact 1 of relay LO(6), the circuit tobe described later for operating the hold magnet of the associated linewhen called, thereby making the first line busy, and opens at contacts 4of relays LO(6) and L(6) the start circuit, previously traced overconductor 001, for seizing a link.

First digit dialed When the calling first line subscriber 300 wasconnected to the first link and relays A(4) and 3(4) operated, as abovedescribed, dial tone was supplied to subscriber 300 in a circuitextending from ground, through the left winding of dial tone transformer501 (which, it will be understood, picks up dial tone supplied by thesource thereof 504 through the right winding of transformer 501), overconductor 405, contact 1 of relay DT(4), upper winding of relay A(4),contact 3 of relay D(4), contact 13 of relay CT(4), ring conductor 300,contact 2 of the switch, to ring conductor 305 of the calling line andthence back winding of relay 2(1).

to battery through the lower winding of relay A(4) as previously traced.

Let it be assumed that the called number is 863, where, it will berecalled, the first two digits 86 represent the number of the calledline and the last digit 3 represents the ringing code applicable to thedesired party on that line 86.

Upon the first open line period (the first pulse of the first digit asthe dial restores to normal), relay A(4) releases. Relay B(4) isslow-releasing and will not release during pulses of a digit when relayA(4) is released. Relay C(4) operates in a circuit extending fromground, over contact of relay A(4), contact 2 of relay B(4), to batterythrough the winding of relay C(4) Relay C( 1), upon operating, operatesrelay C2(5) in a circuit extending from ground, over contact 3 of relay0(4), conductor 401, to battery through the winding of relay 02(5).Relay (3(4), upon operating, extends its operating ground over itscontact 4, conductor 408, contact 6 of busy relay B8Y(5), conductor 505,contacts 3 of relays 83(1), 82(1) and 81(1), to battery through thewinding of relay 1(1) which relay thereupon operates. At this time itwill be noted that the operating ground for relay 1(1) is extended overcontact 4 of relay 1(1) to the left side of the winding of relay 81(1),and the right side of the winding of relay 81(1) is grounded overcontact 1 of relay 82(1), conductor 100, and contact 5 of relay C2(5).Thus relay 81(1) cannot operate.

At the end of the first open line period (the first pulse), relay A(4)reoperates thereby opening the operating circuits for relays 0(4) and1(1), above traced. Relay C(4) is a slow-releasing relay which willremain operated between pulses of any digit but will release betweendigits as will be explained. As soon as the operating ground is removedfrom relay 1(1), relay 81(1) operates in series therewith in a circuitextending from ground, over contact 6 of relay 02(5), conductor 1011,contact 1 of relay 82(1), Winding of relay 81(1), contact 4 of relay1(1), to battery through the Winding of relay 1 (1) Upon the second openline period (the second pulse), relay A(4) again releases completing thesame circuit from ground, over contact 1 of relay A(4), contact 2 ofrelay 13(4), contact 4 of relay C( 1), conductor 408, contact 6 of relayBSY( 5) to conductor 505, as before. Ground on conductor 505 is extendedover contacts 3 of relays 83(1) and 82(1), contact 2 of relay 81(1),contact 5 of relay 1(1), to battery through the Relay 2(1) operates toextend its operating ground over its contact 3 to the left side of thewinding of relay 82(1). Relay 82(1) cannot operate because the rightside of its winding is grounded over contact 1 of relay 83(1), conductor100, and contact 6 of relay 02(5).

At the end of the second open line period (the second pulse), relay A(4)reoperates thereby opening the operating circuit of relay 2(1) byremoving ground from conductor 505. Relay 82(1) now operates in serieswith relay 2(1) over a circuit extending from battery, through thewinding of relay 2(1), contact 3 of relay 2(1), winding of relay 82(1),contact 1 of relay 3( 1), conductor 100, to ground over contact 5 ofrelay 02(5) Relay 82(1), upon operating, opens, at its contact 1 theoperating circuit for relays 81(1) and 1(1), which relays thereuponrelease.

Upon the third open line period (the third puise),,re1ay A(4) againreleases to again ground conductor 505' as before. This ground is eX-tended over contact 3 of relay 83(1), contact 2 of relay 82(1), contact4 of. relay 2(1) to battery through the winding of relay 3(1). Relay3(l) operates, extending its operating ground over its contact 4 to theleft side of the winding of relay 83(1), the right side of thewinding ofrelay 83(1) being grounded over contact I of relay 8! (1), conductormfl,and over' contact 6 of relay C2(5).

At the end of the third open'line period (the third pulse), relay AU!)reope'rat'es' to" remove ground from conductor 5'05 thereby to permitrelay 83(1) to operate in serieswith' relay 3(1). Relay 83(1), uponoperating;. releases relays 82(1) and 2(1) by opening, at contact Iofrelay 83(1), the operating circuit thereof.

Upon the fourth pulse, relay A'(4) releases" to again apply ground to"conductor 555. This ground extends over contact 2' of relay-83(1),contact 5' of relay 3(1)", to battery through the winding of re'lay4('1)*, which rel'ay'thereuporioperates.

At the end of the fourth pulse; relay AM) reoperates to remove groundfrom C'Qhdl'ilCtb'i 5B5 thereby permitting" re'la'yl8l'(1)" to operatein series with relay 6(1) in -a circuit exte d ingi'from battery,through the winding ofrel'ay"4(1"),.c'ontact 3 of relay 4(1), Winding'ofrelays-t), conapply ground to conductor'5'05and theh reoper ates toremove ground" from said conductor. Ground on conductor 505 extendsovercoritacts 3 of relays 82(1) and 83(1), contact'i'of" relay 8H1),contact 4"of'relay"4(1'), conductor 1.01", to

battery throughth'e Winding of r'el'ay",5'(8). Rer.

lay (8) operates and, upon the',reinova1' of ground from'conduc'tor'5fl5 at theendbf the fifth pulse, relay 82(1)i's'operated'in series with relay 5(8') over contact [of relay (8),conductor etc, winding of relay. 82(1) togroundiov'er contact l of relay83(1): and conductor 10,0 aspieyi} ously described; The? operationo'f-"relay- 82(1)- releases'relays'sl (1') and 4(1).

During the sixth'pulse, ground on conductor 555 will be extended overcontact" 3" of relay 83(1), contact 2 of relay'82('1)", conductor 102,contact 51 of relay 5(8)"; to? batter through" the Winding of relay 6(8)which" relay thereupon 0p.- erates. Wheng'round isre'm'OVed" fromcohductor-565 at the endiofithe sixth pulse; relay, 83(1) operates inseries with relay" 6(8), thereby. re- 1easing'relays82'(1) a'nd 5(8);

During the seventhpulse, groundionconductor 585 is extended over contact2"of"relay. 83(1), conductor 103; contact 4 of're1ay '6(8 tobatterythrough the-winding of relayl1(8)'1; which relay operates. When groundiSI removed from" conductor 555% the endofthe'severi hpiilse (when relayA01) reoperates); relay" 8'! (.11) operates in series with relay 1(8)"over contact-5 of relay 1(8), conductor 8,02, winding'lof relay 81(1)",-to ground over' conductor'lfijl', as" reviously. described; Theoperation" of" re1aysm) releases relays 83(1) and 6(8). Relay 1(8); uponoperating, completes 1 a circuit" for operating relay 8W(d) extendingfrom" ground; overhofitactifi 'of relay 82(5), conductor lilil," contactI of'relay l (8) conductor 806i contact9'*o frelay1DT'M), tobatterythrough the" upp r Wihdifig' of relay, 8W( i-). Belay SW14)operates'and' locks" to ground on conductor over its contact 1. Whenrelay 8W(4) operates, a circuit is completed extending from ground, overcontact 3 of relay 1(8), conductor 8S1, contact ll! of relay 8W(5),conductor 4| 5, to battery through the Winding of relay TP'(5). RelayTP(5) may 1110- inentarily operate'in the latter'circ'uitj but, sincethe function of relay TP(5) is to switch the ringing ground from oneside of the called line to the other, depending upon the ringing codedialed (third digit), the operation of relay 'IP(5) has no efiect atthis time, and such relay will release during the recording of theeighth pulse, if any.

During the eighth pulse, ground on conductor 585' is extended overcontacts 3 of relays 83(1) and 82(1), contact 2' of relay 8H1),conductor 1M, contact 6' of relay 1(8), to battery through the upperwinding of relay 8(8), which relay thereupon operates; When ground isremoved from conductor 505 at the end" of the eighth pulse, relay 82(1)operates'in' series with relay 8(8) over contact l1 of relay 8(8),c'oriductor 808, winding of relay 82(1), contact I of relay 83(1)conductor 100, togi'ou'nd over contac't' or relay (22(5). The operationof relay 82(1) releases relays 81(1) and 1(8), thelattei"thus-releasingrelay 'IZP( 5). Relay 8(8) locks also thr'o'ug'h' its lower Winding,Contact it of relay 8"(8'), conductor 384, contact 4'of relayRC9'(5)",c6ritact5 of relay TP(5) conductor 506, to off n'orni'al groundover contact 3 of relay B-(G').

During the ninth pulse, ground on conductor 555 is extended over contact3"of'r'e1ay 83(1), contact 2 of relay 82(1)", conductor 152, contact l8of relay 8(8), conductor 8G5, contact I I ofrelay DTM'); conductor 409;to battery through the upper winding of relay RC "9(5); whichrelay'opcrates and looks through its lower winding, contact 1' of relayRC9(5), contact 4' of relay 0(5), conductor 501, toground over contact Iof relay 13(4). Relay-RC9(5')', upon operating, opens the above-tracedlocking circuit through the lower winding'of relay"8(8')'; When'groundis removed from conductor 505 at the end of the ninth pulse, relay 83(1)operates in series with the upper winding of relay RC'9(5) over contact6 of'relay RC9(5), conductor Bill, windingof relay 83(1), conductor 150,to ground over contact 6 of relay 02(5). Relay 83(1), upon operating;releases relays 82(1) and 8(8).

During the'tenth pulse, ground on'cpnductor 585 is extended overcontact! 'of relay'83'(1), cfon= ductor 103, contact 9'--ofrelayRC9(5-), to battery through the upper winding of relay 6(5); Relay()(5) operates andlocks'through' its lower wind ing, c'o'ntact5'oirelay'tlfi'), conductor 586,130 offnorr nal ground ground over contact3101? relay 3(4). The operation ofrel'ay 0(5) releases relays RC9(5)and-83(1). When ground isrernoved from conductor 505-at the end of thetenth pulse (when relay- A'(4-) reop'erates), relays6'(5) and SWQ)remain operated. 7

Thus at the end of each pulse of the first digit (at the instant relayAm) reoperates) the fol lowingchart shows what relays; are then operatedwith reference'to-the digit dialed:

1 1 It will be recalled that it was assumed that the called line andstation connected thereto were to be identified by the three digits 863.Thus, at the end of the eighth pulse of the first digit, when relay AM)reoperated, relays 82(1), 8(8) and SW05) were operated. When relay AUi)remains operated after the end of the eighth pulse, relay (4) releases,thereupon releasing relay 02(5) after the release delay time of thelatter. Upon the release of relays 0(4) and 02(5) relay BT03) operatesin a circuit extending from ground, over contact 2 of relay 0(4),conductor H, contact 3 of relay 02(5) conductor 588, contact 8 of relaySW03) contact 5 of relay D'IUi) to battery through the winding of relayDTM). Relay DTM) operates and looks over its contact 6 to off-normalground over contact 3 of relay 3(4) Relay DT(3), upon operating,replaces dial tone ground on its contact I by solid ground over itscontact 2, previously traced to the ring side of the calling subscribersline. When relay 02(5) released, the holding ground, over contact 6 ofrelay 02(5), for relay SW03) was removed; but, relay SW03) issufiiciently slow to release to permit relay DTUi) to operate and lockbefore relay SW03) fully releases. The release of relay 02(5) alsoreleases relay 82(1), which was operated in series with relay 8(8) thelatter relay remaining operated through its lower winding under thecontrol of relays R09 (5) TP(5) and 3(5) as previously described.

Preliminar impulses It will be appreciated that if any preliminaryimpulse, due to accident or otherwise, had been received, or if anydigit less than a 7 had been dialed as a first digit, then relay SW03)would not have operated at all since, as above described, relay SW03)operates only upon the operation of relay 1(8) representing the countingof the digit 7. Thus, under the condition where a first digit of lessthan seven pulses is received, neither relay SW(4) nor relay DTM) willbe operated and dial tone will remain connected to the calling linerequiring that a correct first digit be dialed if the calling subscriberdesires an interconnection.

Second digit dialed The second digit is assumed to be 6 in accordancewith the assumed called subscribers line and station number 863. Thereis a punching in Fig. 8 for each line of the switch unit. For instancepunching FL(8) is for the first line, punching IL(8) for theintermediate line, and punching LL(8) for the last line. Punching FL(8)may be traced in circuit over conductor 8| 0 to contact I of the linerelay L(6) of the first line. Punching LL(8) may be traced in circuitover conductor 889 tocontact I of the line relay L(6) of the last line.Likewise, the other punchings, such as IL(8), may be considered to be insimilar circuits with their respective line relay contacts I. Oppositeto these line punchings are arranged some fourteen other punchings 1l(8)to 11(8) and 8l(8) to 81(8) connected respectively to seven back andseven front contacts of relay 8(8). As will be appreciated fromsubsequent description, one of the fourteen punchings will be groundedthrough the lower winding of relay ROI(5) depending upon the first twodigits of the called number. For instance, if, as in the assumed case,the first two digits of the called number are 86, the punching 86(8)will be so grounded as a result of the counting of these two successivedigits. It will readily be seen that the assignment of numbers to linesis simply a matter of cross-connection between a particular linepunching, say punching LL(8) for the last line, and a particular numberpunching, say punching 86(8), as shown by cross-connection 888.

At the end of the sixth pulse of the second digit (when relay A(4)reoperates) as above described, the counting circuit will have effectedthe operation of relays 83(1) and 6(8) in series, with relays 0(4) and02(5) not released yet. Upon the operation of relay 6(8) a circuit iscompleted for operating relay RCI(5) from ground, over contact 4 ofrelay DTM), contact 5 of relay SW01), conductor M2, lower winding ofrelay ROI(5), conductor 589, contact I of relay 6(8), contact l2 ofrelay 8(8), number punching 86(8), cross-connection 888, line punchingLL(8) for the last line, conductor 889, contact I of relay L(6) of thelast line, contact I of relay LD(6) of the last line, conductor 683,winding of hold magnet H(3) of the last line, to battery. Relay ROI(5)operates in this circuit but hold magnet H(3) does not operate due tothe high resistance of the lower winding of relay ROI(5). Relay ROI(5)operates in this manner in series with each line as the pulse countprogresses from 1 to 6, except where a line is busy or a line is vacantas will be explained, none of the respective hold magnets H(3)operating, however.

During the dialing of the second digit arrangements are provided fordisabling the line circuits to prevent interference between suchcircuits, which may try to initiate an originating or incoming call, andthe connection of a link circuit with a line or trunk on an outgoingcall. This is provided by operating the line delay relay LD(6) common toall line circuits. The operating circuit for relay LD(6) extends fromground, over contact I of relay 0(4), conductor M5, contact i of relay02(5), conductor 5l2, contact 3 of relay DT(4), contact 4 of relay8W(4), conductor 416, to battery through the winding of relay LD(6),which relay thereupon operates to open, at its contact, the startcircuit for all line circuits. As will be mentioned later, at the end ofthe second digit relay 0(4) will release followed by the release ofrelays 02(5) and LD(6). The select and hold magnets, necessary forinterconnection of the link and the called line, will be operated in theinterval between the release of relay 0(4) and the delayed release ofrelay 02(5), as will be described. The release delay time of relay LD(6)is greater than that of relay 02(5) thereby insuring that the calledline is fully seized before the start circuit" is again enabled.

When relay 0(4) releases at the end of the second digit a circuit iscompleted for operating the select magnet 08(3) associated with the Outtermination of the link. This circuit may be traced from ground, overcontact 2 of relay 0(4), conductor 4, contact 4 of relay 02(5),conductor 5H), contact 12 of relay DT(4), contact l of relay SW01),conductor 413, contact 6 of relay 1201(5), conductor 5, contact I8 ofrelay 0T(4), conductor M4, to battery through the select magnet 08(3)associated with the Out termination of the first link circuit. MagnetO8(3), upon operating, extends ground over its contact, conductor 589,contact I of relay 6(8), contact l2 of relay 8(8) ,number punching 86(8),cross-connection 888, line punching LL(8) gem-8s for the last line,conductor 809, contacts I of relays L(6) and LO(6) of the last line,conductor 603, to battery through the winding. of the hold magnet H(3)associated with the called last line to which the number 86- has beenassigned by means of cross-connection 858'. Hold magnet H(3) for thelast line operates closing the cross-points interconnecting the lastline With the first link over the Out termination of the-latter. Holdmagnet H(3) locks to ground over contact I of the cross-points, sleeveconductor 368, contact I of relay 170(4), contact I of relay T(5), tooff-normal ground at contact 3 of relay B03). In Order that theoperating ground for the hold magnet I-I(3) will not shunt down relayROI(), the latter is locked operated by a circuit extending from ground,

.over contact 2 of relay 0(4), conductor M I, contact 4 of relay 02(5).contact I4 of relay R09(5), contact I of relay ROI(5), to batterythrough the upper winding of relay RCI(5).

Upon'the operation of hold magnet H(3) of the last line, sleeve groundisextended over contact I of hold magnet H(3-) conductor 309, to

battery through the upper- Winding of the lockout relay LO(6) associatedwith that-line. Relay LO(B) operates to prevent this line frominitiating a call.

It may be noted that the select and hold magnet operation pertaining tothe; selection and seizure of the called line must take place afterrelay 0(4) releases but prior to the release of relay 02 (5) a conditionprovidedfor by the slowrelease delay time of relay 02(5).

Eventually relays 02(5) and LD('6) release. The release of relay LD'(5),as previously indicated, again enables, at its contact, the startcircuit of all line and'trunk line circuits. Relay 02(5), uponreleasing, releases select magnet 08(3) of the first link andreleasesrelay RCI (5). Upon the release of relay 02(5), relay TP(5) isoperated in a circuit extending from ground, contact 8 of thecross-points or" the called line interconnection, conductor 3Ili,contact I of relay @(5), contact- 9 of relay 02(5), conductor 5I3,contact II of relay 5 W), conductor m, to battery through the winding:of relay TP(5). Relay TP(5), upon operati g, releases relay 8(8) andoperates relay SW(4) in a circuit extending from ground, contact 8 ofthe cross-points, conductor 3H contact I of relay 8(5), contact 6 ofrelay TP(5) conductor 5L4, to battery through thelower winding of relaySW) Relay SW01) operates and locks to ground'on conductor 3H) over itscontact 8 and, upon operating, releases relay TP(5). Relay SW), uponoperating, prepares the link circuit to receive the ringing code digit.

The release of relay 02(5) also releases relays 83(1) and 6(8) of thedigit pulse counting circuit of the link,

Called Zine hus'g/ If the called line had been busy thel'ock 'out relayLO(G:) thereof would havebee'noperated as above described. In such anevent or in the event that the called line number 86 is not assigned asevidenced by an open punching 85(8), relay ROI(5) would not be operatedwhen relay cor) releasesat theen'dof the 'seconddi'git. It willberecalled that relay RCI(5) operates to battery through the winding ofthe .holdgmagnet oi a n idle line, but this circuit is open at contacttQfLOQ) itlh in jbusyenre ar RG 0) fails to operate, the previouslytraced circuit "for 14. operating; the selectimagnet 03(3) will, betraced from the armature ofj relay ROI(5.) over contact I (insteadofcontact 6) or relay 1301(5), contact 3. of, the busy relay. BSY(5 tobattery through the upper winding of relay 1352(5), which relaythereupon operates and locks in a circuit over its contact l, conductor5I5, to ground over contact 5 of relay 3(4). Relay BS Y(5 uponoperating, connects busy tone to the calling line in a circuit extendingfrom the left winding of the busy tone transformer 5", over contact 5 ofrelay BSY(5), conductor 5I6, condenser TP02(4.), contact I of relay0T(4), conductor 404, contact I of the cross-points associated with thecalling line, tip conductor 35M, over the line loop, ring conductor 305,cross-point contact 2, conductor 3%, contact I3 of relay 0T(4), contact3 of relay D( l)-, to ground through the upper winding of relay A(4)andover contact 2 of relay DT(4). This should be recognized by thecalling subscriber as a directive to disconnect and to try again. later.

It will be assumed that the called line is idle andhas beenseized aspreviously described,

Third. (ringin code) digit dialed During the dialing of the third orringing code digit, relays 0(4) and 02(5) reoperate as previouslydescribed; Relay 02-(5) looks over its contact i, conductor 52%),contact 8 of relay SWUl), to cff-normalground over contact 4-015 relayD'I(5-) and; contact 3 of relay 3(4). It will be recalled-that the thirddigit in the assumed case is 3. Thus the counting chain at the end ofthe third digit Willbe in a condition where relays 83(1) and 3(7) areoperated in series and are heldoperated by relay 02(5).

When relay 0(4) releases at the end of the ringing code digit, withrelay 02(5) locked operated, a circuit is completed from a ringinginterrupter circuit, which provides a start signal at the beginning ofeach code ringing cycle, over conductor 8I2, over contact 13 of relayR0903),

conductor 5I8', contact 3 of relay SW(4), contact I of relay DT(4),contact 6 of relay 0(4), conductor 4|], contact 8 of relay 02(5),contact 3 of the pick-up relay PU(5), to battery through the winding ofrelay PU(5). Upon the next grounding of conductor BIZ by the ringinginterrupter circuit at the beginning of a code cycle, relay PU(5)operates in the above-traced circuit and locks overits contact l,conductor 5%, to off -normal ground over. contact 310i relaytBM)Asarranged, ringing code 3 requires ringing on the tip side of the line.Theringing. machine was started operating when relay BM) operated. S uchstart circuit extends from ground, over contact 4 v of. relay B (4)conductor 4 I 8, contact '5 of the ringing cut-on relay R0O(5), overgenerator start conductor 52 I. The ringingmachine will be stopped bythe answer of the called party by the operation then of relay R0O(-5),as will be explained. In order that the ringing shall be applied to thetip side of-thecalled-line, relay 3'('I),'upon operating, operates thetip party relay Tl?(5) in a circuit extending from ground, over contact2 of relay 3(7), conductor contact IQ of relay SW01), conductor Me,tobattery through the winding of relay TPGE) C lled; par y ringinRinging code digit 3 requires. a certain ringing codetobe applied tothetip side ofthe line. The code is supplied over conductor 843 from theringing generator, contact-3 of relay 3 (l)=, conductor 105, contact 4of relay RCI() contact 2 of relay 'I'P( 5) contact 2 of relay PU(5)contact 1 of relay RCO(5), conductor 519, contact 5 of the called linecross-point contacts to the tip conductor 311 of the called line to ringthe particular desired subscriber on that line. Ringing ground issupplied over conductor 522, lower winding of relay RCO(5), contact 2 ofrelay RCI(5), contact 4 of relay TP(5), contact 1 of relay PU(5),contact '1 of relay RCO(5), conductor 523, cross-point contact 6, to thering conductor 312 ofthe called line.

Audible ringing is returned to the calling subscriber from conductor519, through condenser ARCZUi), conductor 4114, contact 1 of the callingsubscribers cross-points, to the tip conductor 354 of the calling line.

Called party answers tip side of the called line and disconnects, at itscontact '1, the ringing ground from the ring side of the calling line. Acircuit is completed for operating relay DU!) extending from ground,through the upper winding of relay D(4), conductor 516, contact 2 ofrelay RC'O(5) conductor 519, cross-point contact 5, tip conductor 311 ofthe called line, over the line loop, ring conductor 312 of the calledline, cross-point contact 6, conductor 523, contact 5 of relay RCO(5),conductor 524, to battery through the lower winding of relay D01). RelayD(4) operates and, in so doing, reverses at its contacts 2 and 4 thepreviously traced ground and battery connections to the calling partysline through the windings of relay A(4).

Talking battery is supplied to the calling line through relay A01)Talking battery is supplied to the called line through relay D(4) Thetalking path may be traced from tip conductor 3135 of the calling line,over cross-point contact 1, conductor 4134, contact 1 of relay CT(4),condenser TPCZUJ) conductor 516, contact 2 of relay RCO(5) conductor519, cross-point contact 5, tip conductor 311 of the called line, overthe called line loop, ring conductor 312 of the called line, cross-pointcontact 6, conductor 523, contact 6 of relay RCO(5), conductor 524,condenser TPC1(4), contact 13 of relay CT( 1), conductor 305,cross-point contact 2, ring conductor 305 of the calling line, and overthe calling line loop back to the tip conductor 3114 of the callingline.

Called party disconnects first Since the link circuits are under controlof the calling party, if the called party disconnects first relay D(4)will be released to restore the normal direction of battery supply tothe calling line; but, the other relays and hold magnets will remainoperated until the calling party releases. Upon the release of relayD01), ground which had been supplied to discharge condenser TC(4) overcontact 5 of relay D(4) is removed to permit the link to time out andrelease, as has been described,

if the calling party does not disconnect prior to the time-out delaytime.

16 Calling party disconnects When the calling subscriber disconnects,relay A01) releases to in turn release the off-normal relay B01) Therelease of relay 13(4) effects the release of all relays of thelinkcircuit and of both hold magnet H(3) of the calling and called lines.The link assignment relay L5(4) will be the last to release to restorethe first link to availability condition.

In the event that the called subscriber has not disconnected, theassociated hold magnet, upon releasing, completes the circuit foroperating the associated line relay L(6) That relay L(5) will operatebefore the slow-to-release lock-out relay LO(5) can release thereby tolock relay LO(5) operated over contact 3 of that relay LOGS) and contact3 of relay L66) to ground through resistance LR(6) Thus the calledsubscribers line will be placed in a locked-out condition until hedisconnects.

REVERTING CALL-SAME LINE The disclosure is arranged to handle revertivecalls upon the dialing of the digit 9 followed by the ringing code ofthe called subscriber.

On the first digit 9, the counting chain of Figs. '7 and 8 will becounted up, as previously described, to operate relays S3 ('1) RC9 (5)and SW01). Immediately at the end of the first digit 9, the followingrelays will be operated as above described: lock-out relay LO (5) of thecalling first line where it is assumed that subscriber 380 is callingsubscriber 313; hold magnet H(3) of the first line; link assignmentrelay LI(4) under the assumption that the link was idle when the callwas made; and, relays A01), B01), DT(4), C( 1), SW05) and C2(5) of thelink circuit. Upon the release of relays C( 5) and 02(5) during theinterdigital pause, relay BT03) operates as before releasing relaySW01), and a circuit is partially completed for operating the busy relayBSY(5) if the second or ringing code digit dialed is greater than 9,which could be only an error. Such circuit would, under suchcircumstances during the ninth open loop period, be traced from groundon conductor 5%, contact 3 of relay S30), contact 2 of relay 52(1)conductor 102, contact 18 of relay 8(8), conductor 805, contact 10 ofrelay DT(4), conductor 419, to battery through the lower winding ofrelay BSY(5).

It will be assumed that the ringing code required to call the calledparty 313 is the digit 4. Upon the dialing of the digit 4, relay A(4)releases and reoperates to follow the open loop pulses as before andrelays C(4) and C2(5) reoperate and remain operated for the duration ofthe digit as previously described. Relay 02(5), upon operating,reoperates relay SWUi) in a circuit extending from ground, over contact6 of relay C2 (5) contact 3 of relay RC9 (5), conductor 525, contact 8of relay DTOl) to battery through the upper winding of relay SW01),which relay operates and locks as before, in turn locking relay C2(5)operated. Relay 02(5), remaining operated, locks the digit 4 in thecounting chain where relays 81(1) and 1(1) remain operated after the endof the ringing code digit. Relay SW01) applies ground over its contact12, conductor 421), and contact 8 of relay RC9(5) to the off-normalground conductor 5116 to insure a holding'condition in the link circuitduring ringing.

At the end of the dialing of the second digit 4, upon the release ofrelay C( 1) with relay C2(5) held operated as described, relay BSY(5) isop- .eratedto apply a busy signal to the calling line as l'l' 1 I adirectivetothe calling," party to disconnect. preparatory tosetting upthe ringing condition. Relay BSYQB'J' operates: ina circuit extending,fromground, over contact 2 of relay: C(U, con-- ductor- I, contact 4 orrelay C2659, conductor 5H1, contact I2 of relay BT64), contact- 2 ofrelay SW64); conductor 21 contact 2 of relay 124C965)" to batterythrough the lower winding of relay BSY('5) Relay BSYIE)? looks. over itscon tact fi, conductor 515, to: ground over contact 5.

of relay B64), Relay BSY('5) applies-busy tone; toi-thecallingline aspreviously described; At; its contact 6, relay BSY65) opens the pulsing:con! ductor 505 to preventthe: opening or the line reap,-

scribed, under theeco-ntro l of relaysSzWQd) and RQ9165:).-, relay R.9(5;'): remaining operated after i the release; of? relay BM.) in acircuit over-contact; 1 of: relay EJ619652), contact our relay M51),con--- tact; Z or relayxC2l15) conductor 5,26,;to; ground at contact 501"? relay D 64. Whenrelay' B(.4-)I re leasesit releases relay BSYG5):before. relay 63(4),

releases;

Ktthe beginning of the ringing cycle; as previeousiy: describechgroundis applied torconductor 8I12and ist extended over contact 2 of relay'R6965), conductor 521 contact 6' or. relay B("4).,, contact. of relay:SWM), contact I? of relay Dlt l-l contact 8 of relay CM), conductor 41:1contac-t 8' of relay {32 (5) contact 3 of relay PU(5) to battery throughthe winding of relay PUG- Relay W659 operates and locks to: oft-normalground on conductor 506 over its contact 4 Re lay PU CS), uponoperating, operates the cut-.- throughrelay CF'G i) in-orderto connectthe outgoing tip and ring conductors 5I9 and 523 tothe incoming tip andring conductors 4 and-.3 05 so the the latter will carrythe ringingcode. The

circuit may be traced from ground, over contact I I I of relay RC9(5),contact 5 of relay PU(5) con-- ductor 528, to battery through the upperwindingrof. relay 013(4) ,whic-h relay operatesand locks throng-h; itslower winding, its,- contact 5, its;v con tact 8, conductor. 529,;lie-ground: over, contact 10;

ot relay- 131C565); The; latter groundon conductor 529 isextendedto-the-sleeye conductor 493: of, the incoming unit oi the linkto holdthe calling line hold magnet H("3)- operated, ground on conductor'529'bein'g so: applied over minteuct-v 2 of thetime-IE out:relayTQUIJ and: contact 2.05; relay LlM-l Rel'ayLtfMt): isheldoperate'dito the. same ground over contactid ofrelayCflY'At);

' Ringing code -4;, as arranged; requires ringing:

entire ring side or: thelinesorelay TP(5)'. will not;

p contact Iofrelay-TPQ5), contact 2 of relay- PUCE),

contact I of relay RG06), conductor- 5I9 contact; 2 of relay CTUI),conductor 4M, cross-point: contact I of thecross bar switch, totheti-pconductor 304' of thecalling; line. The ring conductorof the callingline is connected over crosspoint contact 2-, conductor 305, contact I2of relay CTN), conductor52-3, contact I of relay RCOG-j), contact Iof'relay PUG), contact 3 0i relay TP-(5)',

contact 4 of relay RCI(5)'*, conductor T05, contact 18 2 of relay 4:('I)a, conductor 813 to the ringing: code generator;

At the end of each ringing cycle relay RG16) is operated momentarily bya. short, impulse of ground from the reverting call impulse generatorover conductor 530, contactl of r'elayPU (151) con-.-v tact 5 of relayRC9(5) to battery through.theurn perk winding 01: relay ROI (5)1. RelayRCICd); op,-

erates and: remains operated: beyond the duration or the impulse, due toits slow releasing character, for a length of time short. ot'the end ofthe giing cycle, whereupon, relay 301(5), releases to permit the nextringing cycle to go over the line as; abovedescribed; the lookingcircuit: for: relay RCICEr): being openat contact I 4 of relay-R6915Duringthe time relay RIl('5l-)l is; operated. con-l tinuous; ringing. isapplied to. the opposite side or the calling line, (tip side) to givethe calling; sub-J,

scriber, if his. ringer 18: connected to: that side air opportunity to.knowv that the-called party is be-- ing signaled and anopportunityto.knovw when that party answers, the latter causing thecessation ofringing; as previously described. The-previous ringing ground applied tothe. tip sideof the: line over contact 2 of relay RCI(5.) is replaced bycontinuous ringing voltage over conductor-53lf and contact 31 of relayRCI(5 )l. The. previous cotl'er ringing voltage applied to the ring sideof the lineover contact 4" of" relay- RCI(5) is re-- placed by ringing"ground over conductor 522,;

lower winding oi relayRCol-i) and contact 5 of relay B0145 This ringingof the called subscribers code on the ring side of the line followed,near the end of Ethe -ringing: cycle, by a short ringing on: the tipside of the line continues until the called sub.- scriber answers, oruntil the calling subscriber disconnects to release the link.

A Called partyanswers.

When; the called party answers, the; ringing cut-old relay B63015): is.operated over thetdirectcurrent bridge" of the lineat the called party:substation in a. circuit extending from ground on.

= conductor 5.22", through the lower winding of? relay RCOCSJ, contact 2of: relay RCI C5), thence,

over the line. as. previously. traced. for theringing current, backioyercontact; 4 of relay RCI (5)-,.and over conductor 10.6 to the codegenerator, Relay RCO GE'I locks over its contact 3 to ofisnormal.

ground on conductor 5%. Relay ECO-(5),. upon.-

operating', diseonnects, at itscontacts I and; 'l:,=the ringing: circuitfrom the line and. operates relay DIME); in; a circuit extendingiromground, through the upper winding of relay DH) conductor SIG; contact 2vofrelay RCOr(5)., conductor 51:9, contact 2 of relayCT'M)", conductor404', crosspointcone.v

tact i, tipconductor 304, over the closed line loop ring conductor305,0ross-point contact 2, c"o'ndu'c tor 3115, contact- I 2 ofrelayCTfl), conductor 523 contactt of relay RCO 5), conductor 52 E, tohat I tery'through the lower winding ofrelay Dt l Relay D(-4)-, uponoperating, releases relay- RC9(5) which, in turn, removes ground fromthe 1 d'uctor 40 5 of theswitch unit therebypermitting hold magnetH'Gi3=)= to-release; in turn opening the cross point contacts; Releaseof hold magnet H63) reoperates the liner-clay L(6-) of the calledlinether'eby locking operatedthe associatedlockout. relay L005) aspreviously described.

V The release of" relay RG96 also removes ground from the sleeve om-TRUNK CALLINCOMING As shown, there are four trunks terminating in,

four verticals of the switching unit. These trunks, of-which only thefirst and last of the group are shown, may also terminate in distantmanual orautomatic oflices and may handle incoming or' outgoing callsfrom or to such. office. ofdce may switch such trunks to other switchingunits. in other communities, or to other exchanges.

A call incoming over one of such trunks is handled at the switching unitsimilarly to a call originating on a line appearing in a vertical ofsuch unit.

It will be assumed that a call is incoming over the last trunk, circuitsof which appear in Fig.

10. When the trunk conductors I000 and IIv are bridged to indicate anincoming call, the trunk line relay TL(I0) operates in a circuitextending from ground, through the lower wind ing of relay TL(I0),conductor I002, contact 3 of the hold magnet H(3) associated with thelast trunk, conductor 3I4, contact 4 of relay TOT(I0), conductor I000,over the closed loop ofv the trunk, back over conductor IO0I, contact Iof relay TOT(I0), conductor I003, contact 2 of hold magnet H(3),conductor 3I5, to battery through the upper winding of relay TL(I0).Relay TL(I0), upon operating, operates the line supervisory relay LS(6)in a circuit extending from ground, over contact I of relay TL( I0)conductor I004, conductor 900, to battery through the winding of relayLS(6), which relay operates, as previously described, to place anycalling line on lock-out condition if such line should operate its linerelay L(6) while relay LS(6) is operated. This prevents interference bylocal calling lines with the setting up of the presently consideredincoming trunk call.

.Relay TL( I0) upon operating, completes a circuit for seizing an idlelink circuit. Such circuit extends from ground, over the contact ofrelay LD(6), conductor 504, conductor 90I, contact 5 of the trunklock-out relay TLO(I0), contact 3 of relay TL(I0), to the startconductor Bill, as in the previous case of a calling line, over contact6 of the link assignment relay LI (4) if that link is idle, or overcontact I of relay LI(4) to a corresponding contact 6 of the firstreleased relay L-(4), conductor 400, to battery through the upperwinding of relay RCI(5) of the idle link circuit to be seized.

When the link circuit is seized, just as was the case with the callingline previously described, the in select magnet IS(3) is operated toreturn ground over conductor 302, contact 4 of relay LI (4) andconductor 402 to operate the hold magnet of the calling trunk. Ground onconductor 402 extends over contact 2 of relay TL(I0), contact 4 of relayTLO(I0), conductor I005, to battery through the winding of hold magnetH(3) associated with the calling trunk. Hold magnet H(3) upon operating,locks to sleeve ground over Such I cross-point contact I5, releasesrelays TL(I0) and LS(6), and extends sleeve ground over its contact I,conductor 3I6, and contact 2 of the trunk-out control relay TOC(I0), tobattery through the upper winding of relay TLO(I0). Relay TLO(IO)operates, looking over its contact I to ground on conductor 3I6 justtraced.

Subsequent circuit operation is the same as in the case, abovedescribed, of a local call within the same switch unit, line relay TL(I0) and lockout relay TLO(IIl) of the incoming trunk line circuitcorresponding to and performing similar functions as line relay L(6) andlock-out relay LO(6) of the calling line circuit. The link will countand register the called digits and will,

responsive thereto, set up the interconnection over its in and out unitsas has been described above.

No provision is made to lock out simultaneous incoming trunk callsbecause it is assumed that only one such call will be made at any giventime under the control of an operator or automatic central ofiiceequipment.

In the event that the link circuit times out,

as has been described with reference to tube,

TT(4) and relay TOM), hold magnet H(3) will be released reoperating thetrunk line relayv TL(I0). Since relay TLO(IO) is slow releasing, thereoperation of relay TL(I0) will lock relay TLO(I0) operated beforerelay TLO(IEI) can release upon the release of hold magnet H(3). Thislocking circuit, under those circumstances, would extend from ground,over contact 4 of relay TL(IB) and contact 2 of relay TLO(IIJ) tobattery through the lower winding of relay TLO( I 0). Relay TLO(IO)would retain the trunk line circuit locked out until the incoming trunkline was opened long enough to permit relay TLO( I 0) to release. As wasthe case with the lock-out relay LO(6) of a calling line circuit, relayTLO( I 0) prevents that particular incoming trunk from seizing an idlelink until the trunk has been cleared.

At the end of the conversation when both parties disconnect all circuitsrevert to normal in the same manner as has been described heretofore.

- TRUNK CALL--OUTGOING An outgoing trunk call arises when one of thesubscribers whose lines terminate in verticals of the switch unitdesires an interconnection with a subscriber whose line is accessiblethrough only a central ofiice, either manual or automatic.

seizing an idle link When relay 0(5) operates, a circuit is completedfor operating the line delay relay LD(6) to open the start circuit overconductor GUI for all calling lines and all calling trunks. This circuitmay be traced from ground, over contact I of relay C( 5), conductor 4I5,contact I of relay C2(5), contact 6 of relay 0(5), conductor M6, tobattery through the winding of relay LD(5), which relay thereuponoperates to open, at its contact, the previously traced link seizurestart circuit over conductor 60I.

When: relays 6G4): and. 621(5); release; after: the end; of firstdig-it; zero, the select: magnet: 018635)? of the out? unit of: thefirstilink circuit is: operated to: prepare for the interconnectionv ofthe li'nlc with. an idle trunk circuit. Select magnet 08(3) operates ina. circuit extending from ground; over contact 51 of relay 02(5),contact: 2 of; relayBSiHE): contact'a off relayuifiw, cone ductor 5| I,contact lt oii relay CTN)", conductor 4, to battery throughtherwi-ndingoi select magnet 03 63) Relay'DIM )r. is also. operated. byrelay SW6d): operated and relays. C14,)? and; C265); released.asrpreviously described;

Sez'ez'nd an idle Select magnet OS 03"), upon operating; returnsgroundover its contact, conductor 509 ccntact 1- ofrelay 0(5), conductor532, to battery through the trunk-out control relay TOC'G I0 which opcrates. This rl'ayTOG'lflt common to an of the trunks terminatingattheswitching funit. l-t'elay TOC(-l 0 upon opera-ting, provides alocking circuit for relay LD(0-)- from ground, over contact of relayTOml fll 'to conductor' l l-fi. ReIayTOCU U) operates the trunk-outrelay TGT(9):-' or TOWN); etc: of the first idle trunk a circuitextendingfrornground; over contact il -of relayTOC( l0) ,"cond-uctorI006, contact It or relay TLOGS' F ('assn-rrii'ng the first trunk'to-"beidle), to -batterythrough the lower windings? relay PO-T69) of the firsttrunk. if the first trunk had been busy relay 1 (9)- thereoi would havebeen operated, whereupon the above" circuit would have extended over"contact- 3 of" relay TLGQQN, front contacts of'all other operated re--l'ay's- TLO conductor 90!, contacts of relay T130610; cf'the last trunk(er-a back contact of the first idle trunk) to battery through the lowerwinding ofthe relay TQI(=-) of that first idle trunk; such'asrelay-TO- I-(l fldh -It will beessinned that the 'first trunk is idleand that relay TOT-W90 thereof operates. 1

-'Relay- 130N90 uponoperating, operates the associated hold magnet H43)from ground, over ccntact of relay TOT(-9)-, conductor 90 3', to batterythrough the winding-of hold} magnet Hi3) of t'he firsttrunk. Hold magnet1 1(3) operates to connect the trunltwiththe link over' the crosspcintcontacts '9 to I 2. The operating groiind forhol'd magnet HK3J isextended from conductor 903,: over cross-pointIcontact: H, to thesleeveconductor 3:08 ofz thewout unit. of the lir'ilrcir'cuit.v Upon theclosing. of the cross-points; relay CT 4 is operated in av circuitextending from ground,

over cross-point contact. IE2, conductor 3H),. con! ta'ctZ of relay02(5), contact I ofi relay BSY(5), contact" 10 of relay C2.:'(15:),,conductonfiw, tobattery through. the. upper winding of relay CT); RelayCFIKA) operates? to? interconnectthein and: out. units ofthe linkcircuit. and to disconmeet; any elements of the link. circiutx bridgingthisxitalkingipath The ground on. sleeve: con.-

ductorxllnfl is: extended over. contact I: Jot the: time outrelay TOM);contacts: 6 and 03 ofrelay conductor 520,.contact 2 of. relay TOM),ecer'c'ontacti 2 of relay Ill-(14). to-slfeeve conductor 403 012 the:in? unit: of this link; Relay CT) I'oc'kslover itscontacttQl to; thissleeve: ground. on:

22,. lays CT(4:): and Ll.(.4'.),.which, as: abmze! mentioned, are lockedto sleeve ground. under-the control. of relay TO:(.4);.. The. operationoi'rel'ay 011(4)" releases select magnet 03(3); and the release ofselect magnet, 08(3) and relay Mix releases the. trunk-outv controlrelay TOUGH).

Upon. the. release of relay T060 00 lock-out relay TLO(.9:) of: theseized trunk is operated: in. acircuit: extending from. ground. on. thesleeve conductor 3.08" of: the. link, over cross-point comtact I I,contact. of hold magnet H(3) conductor 3, contact 1' of'relay TOCU'B)",conductor I001, to batteryathrough. the upper. winding of relay1130(9)... Relay TLO (9*) operates andl'ocks: over its: contact I. toground: on: conductor 0|? indem pendently: of; relay TOC(1I0);.. RelayTLOQQ); transfersatits contact 3-,. as above: described, the, start?circuit: to the. next. idle trunk circuit.

Relay: TAGS") operates over the.- calling, line loop in a circuitextending. from. ground through the. upper winding of relay TA(9);-,.contact of relayx'FOT(.9)i, tip conductor 904 of the: trunk line.circuit, cross-point contact 0-, tip:- conductor. 5l'9." of? the linkout unit, contact. ofirelay:

CTMi) of: the link, tipconductor 404. of the link.

in zunit', cross-point contact I, tip.- conductor 304 of the callingline circuit, over thecalhng; line loop, ring conductor 305 of thecalling line circuit, cross-point contactZ, ring conductor-306 of thelink in unit,; contact ll of. relay CT (4-) oithe link, ring conductor523 of the, link out unit, cross-pointcontact. L0, ring conductor 3l0 ofthe trunk line. circuit, contact 8- of relay TOTCQ), tobattcry' through.the lower winding, of relay. Tam). Relay TAG-l upon: operating, operatesrelay TB(9-)' in an obvious circuitover contact 3 of relay TAGH'). Relay'IB-(li), upon operating provides av locking circuit over contact I ofrelay TB(0) i or relay TOTCS which is effective. be fore. theoperationofrelay TLO(-.9 which opened theoperating circuit for relay TOT(9).

Central oi fica seizure Relay TA (;9 upon. operating, completes. a.bridge across the outgoing, tip and ring. trunk conductors 905 and 906fromcond-uctor 905,,cver contact 5 of relay TOT(9), contact I of relayTA(9), contact I of relay TC(9),.through.indiic.- tion. coil I-C(.9),contact 3 of relay TC (.9), contact 2. of relay TA.(9.) contact-6 ofrelay TOTCS), to.- conductor 906'. If the; distant termination of thetrunk. conductors 905 and 906 isin a switchboard. ata-m-anual ofli'ce,this bridge is effective-to light a. lamp thereat. If. the dist-antterminaticnli's in. an automatic ofii'ce, this. bridge is effectivetoop.- erat-e. an. incoming selector or line finder, etc, thereat whichmay return dial tone to the calling subscriber as a directive to dialthe number of the called party. In the event. oipa. manual office,aswill. be appreciated, verbal directions to an operator will supply thedesired calIedp-artysd'esignation Dialing called number If the centralcffice: isan automatic exchange, the calling subscriber will beconnected thereto,

as above, whereupon he must dial the called num-:.. ber; Upon the-firstopen line loop during the first operated until relay TA.(9-) reoperates'for a ma

